Field
The disclosed concept pertains generally to electrical disconnects for interrupting or breaking an electrical connection. More particularly, the disclosed concept pertains to electrical disconnects related to medium voltage auxiliary devices.
Background Information
In an electric power system, switchgear is the combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is directly linked to the reliability of the electricity supply.
Typically, switchgear in substations are located on both the high-voltage and low-voltage side of large power transformers. The switchgear on the low-voltage side of the transformers may be located in a building, with medium-voltage circuit breakers for distribution circuits, along with metering, control, and protection equipment. Switchgear commonly includes medium voltage disconnects for electrically connecting (and disconnecting) auxiliary devices (e.g., without limitation, voltage transformers, control power transformers) to a main power feed. Such disconnects include separable contacts which are movable between a closed position, in which the contacts are electrically engaged and thus current is provided to the auxiliary device, and an open position in which the contacts are spaced a suitable separation distance apart, thus isolating the auxiliary device. Movement of the contacts is typically carried out by a racking mechanism which moves one of the contacts a required separation distance from the other fixed contact. In known arrangements, the contacts may require separation distances in the range of about five to twenty inches (depending on the voltage) in order to safely separate the contacts and avoid partial discharge and arcflash. Such generally large separation distances, as well as the racking mechanism(s) required to move the contact such distances, require the use of generally large housings which thus limit the quantity of such arrangements which may be used in a particular facility.
There is thus room for improvement in electrical disconnects, and particularly in electrical disconnects for use in electrically connecting an auxiliary device to a medium voltage power source.